A verified layout for the Nixie SMPS, I just built and tested it today. It's putting out 313 volts without a load. I haven't added the snubber yet, I want to experiment with that part. The snubber is made up of the 2.2K resistor and the 100pF cap in the Nixie schematic. I've an idea that changing the snubber values slightly will keep the B+ higher, so I thought I'd build the main part and hook it up to my breadboard to test different filterings. I used two 100uF caps instead of the 330uF, mainly to save on space.

The SMPS is for my next amp. I've got some 12AX7 and 12AU7 left over from my Valvecaster builds last year, and I bought a bulk lot of Fender Reverb Transformers (for my Murder Ones), so I thought I'd try a SE amp with 'proper big tubes' and a SMPS.

Here's a variation on the 555 SMPS with the addition of a negative charge pump section. Probably of interest to only one person on the planet (me), but developed so I can play with negative grid biasing my 5902 beam pentodes. Verified today on the breadboard. The red stars indicate where it is possible to tap off -11.5 volts and -22 volts, possibly useful for negative grid biasing other tube types.

It looks like a snubber circuit to me which goes in parallel with the FET's drain and source terminals. Or in this case, because you've got voltage-mode control, it goes from the drain to ground. These can increase efficiency in the FET by 20-30%, sometimes more with excessively ringing circuits!

I was thinking that it should be possible to double the ma output by dupilcating the IRF740, snubber, inductor, diode and reservoir cap. ie two parallel SMPS running from the same 555. Obviously the current draw would be significantly higher, but using each of the parallel outputs to drive one dual triode (in a two dual triode design) should give significantly higher voltages and increased performance before saturation of the inductors occurs.

Neat design, but I do wonder why you've connected the negative grid biasing circuit to the gate of the mosfet. As long as there is virtually no load on the negative rail you will be fine else it will reduce the efficiency of the mosfet because the gate isn't driven hard enough. Wouldn't it be better to connect the negative charge pump to the drain of the mosfet?

I was thinking that it should be possible to double the ma output by dupilcating the IRF740, snubber, inductor, diode and reservoir cap. ie two parallel SMPS running from the same 555. Obviously the current draw would be significantly higher, but using each of the parallel outputs to drive one dual triode (in a two dual triode design) should give significantly higher voltages and increased performance before saturation of the inductors occurs.

You would have to sync the two oscillators to prevent beat frequencies from occurring. Just being 30 Hz off is enough to give you audible noise..

Also, I'm not sure how well a direct duty cycle supply will handle being paralleled. Current mode supplies are good at this because both can sense when the load has changed and will adjust accordingly. Direct duty cycle control OTOH just knows that more current = more duty cycle. One of the supplies may be able to try to pull too much current and fail. It may not be a problem with what you're trying to do but it's something to be aware of with simple switchers like these.

A simple circuit to power a NEON lamp. Primarily used to test neons where safety is a requirement. The R1 - R2 - C1 circuit determines the NE-555 to oscillate producing a voltage at Pin 3 driving the small 8 ohm transformer's primary windings, the secondary windings are 1K ohms. It works. This results in a ratio of 125 times gain, however we all know that's not going to fly. Losses ?? The theoretical voltage of 500 Volts AC passing through R3 10K dropping to around 180V AC thus striking the gas within the neon and lighting it. This circuit was designed for pocket use.